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NASA's huge Curiosity rover is just days away from its highly
anticipated, anxiety-inducing landing on Mars.

Curiosity, the centerpiece of NASA's $2.5 billion
Mars Science Laboratory mission (MSL), is due to touch down
inside the Red Planet's Gale Crater on Sunday night (Aug. 5).
Curiosity will search the Gale area — including Mount Sharp, the
3-mile-high (5-kilometer) mountain rising from the crater's
center — for clues that Mars is, or ever was, capable of
supporting microbial life.

The 1-ton Curiosity is so big that engineers had to devise a new
landing method for the rover. It will be lowered to the Martian
surface on cables by a
rocket-powered sky crane, which will then fly off and
crash-land intentionally a short distance away.

SPACE.com caught up recently with MSL chief scientist John
Grotzinger, a geologist at the California Institute of Technology
in Pasadena. Grotzinger discussed how it feels to have landing
right around the corner, what Curiosity might discover and how
much is riding on this mission for NASA. [ How
Curiosity's Nail-Biting Landing Works (Pictures) ]

SPACE.com: How does it feel to be so close to
landing?

John Grotzinger: At this point, it's kind of
what you would imagine. Everybody has been really going flat-out,
and there are a lot of processes that we've sort of divided up
and are responsible for and hoping to reach closure on —
everything from things that relate to tactical planning and how
we're going to do the final bits of staffing for the first six
sols [Martian days], the first 20 sols, the first 30 sols.

I would say overall, everybody is ready. We've been preparing for
this, most of us, anywhere between five and eight years of
continuously and increasingly hard work. And at this point, we're
just excited to get down on the ground and get going.

At the same time, we're nervous. We're nervous about EDL [entry,
descent and landing], we're nervous about the successful
operations on the surface. But we're ready for it.

SPACE.com: You're landing in a very interesting place, so
the stuff you do while checking out the instruments could be
scientifically valuable, right?

Grotzinger: Right. It's kind of cool that we're
landing where it looks like there's an alluvial fan that
undergoes the transition to this high thermal inertia unit,
whatever that is.

So we've got one unit that we think we know what it is, everybody
tends to agree on that, but the high thermal inertia unit —
nobody knows what that is, and we're going to land right on the
contact between the two.

SPACE.com: How long after landing will it be before
Curiosity starts heading off to
Mount Sharp? A couple of months — is that the
ballpark?

Grotzinger: Yeah, I would guess. [MSL project
manager] Pete Theisinger likes to ballpark that we're going to
probably be done with the instrument checkout and really be ready
to drive and do opportunistic science without a lot of further
restrictions probably on the order of 60 to 90 sols.

I support that. It's a conservative estimate, and purposefully
so. And with luck, if everything goes well, we could start quite
a bit sooner than that. But I think the team has discovered that
on the way to Mount Sharp, we probably will not want to just hand
the keys over to the rover drivers and say, "Just get us there."

Now, it might be that after we do some analyses, we find out that
it's pretty uniform, in which case we would want to do something
like that. But in the very beginning, we really want to try to
characterize these units that are in the landing ellipse, just to
make sure we don't miss something that's real exciting.

SPACE.com: So do you guys have a sense of what Mount
Sharp is, and how it formed? There's really nothing like it on
Earth, is there?

Grotzinger: No, not really. In one go, you have
flat-lying strata that are 5 kilometers thick. There's nothing
like that on Earth. So it makes it kind of hard; we don't really
know what's going on there.

SPACE.com: What's the current best thinking about how
this mountain took shape?

Grotzinger: I guess the consensus viewpoint is
that the crater impact basin formed, and then after that water
was available, at least on an episodic basis, and sediments
accumulated. And they were either altered in the presence of the
water or, alternatively, minerals in the water precipitated out.
But one way or the other, they seem to have accumulated in the
presence of water. [Photos:
The Search for Water on Mars]

Initially, there were phyllosilicates that formed, mixed in with
sulfates, and then later on it seems to be pretty much pure
sulfates. And then after about 700 meters, we cross a contact and
go into the rest of the mound, which seems to be built largely of
strata again, but they A) do not show hydrated mineral signatures
and B) in the upper reaches of Mount Sharp, they show very
rhythmic bedding that's been discovered elsewhere on
Mars and we think relates to climate cycles. As the climate
goes through its cycle, wind pattern changes, and you deposit
wind-blown materials in kind of a rhythmic pattern.

Something happened on Mars, and it went dry, and that's what we
have today. The question is, what was that event? What was that
trigger? What happened environmentally? My hope is that we'll get
some insight into this Great Desiccation Event.

SPACE.com: What are some other Mars mysteries Curiosity
could help solve?

Grotzinger: The materials that are in the
landing ellipse — because of the alluvial fan and by inference we
think the high thermal inertia unit — may have had something to
do with water. That package of the alluvial fan plus the high
thermal inertia — we have two options for that.

One option is that these are the very oldest materials at
Gale Crater. So when we drive over to the base of Mount
Sharp, if we get the right geological information, we may see
that this unit extends under the mound, and it is the oldest unit
and therefore this wet period of time in the history of Mars is
consistent with everything we've known all along.

But what happens if those materials that we land on, with the
alluvial fan and the high thermal inertia unit — what if they're
the youngest thing at Gale Crater? That would be very exciting,
because that would suggest that Mars maybe has a more complex
environmental history than what we imagine.

We tend to look at everything that looks wet and say, It's very
old. And we tend to look at things that are dry and say they're
younger. But maybe there were periods of time that were young and
also wet. That would be really cool. [ 7
Biggest Mysteries of Mars ]

SPACE.com: In light of the
recent funding cuts to NASA's planetary science and Mars
programs, do you feel any extra pressure for Curiosity to
succeed? NASA officials have said they're hoping this mission
helps reinvigorate the Mars program by exciting interest among
the public and politicians.

Grotzinger: I would say it's impossible not to
worry on behalf of the Mars program. In terms of the tactical and
strategic planning that we do, nothing will change that. Our
objective is to go out and examine the goals that were stated for
the mission at the outset and use our payload and rover as best
as possible to try to achieve those goals. And I think that if
we're successful in achieving those goals, the tide will rise for
everybody.

So from that point of view, I don't worry about it. But what I do
worry about is, if the pace of discovery is slow, if the Gale
Crater and Mount Sharp field areas turn out to be a more
difficult nut to crack than we think, people may feel that
opportunities are being lost.

So that's why we all go out of our way at the beginning to ask
for patience. We expect the story to be difficult to decipher. On
the other hand, I have confidence that when we do figure it out,
it's going to be a great story, and, like I say, I think the tide
will rise for everybody. [ NASA's
2013 Budget: What Will It Buy? ]

SPACE.com: If something goes wrong with this mission,
will the Mars program suffer?

Grotzinger: Yes, of course. I think if we are
fatal on landing, that will have a very negative influence. It's
going to force people to look back and ask if it's possible to
achieve these very complex, more demanding missions from a
technological perspective. How can you talk about
sample-return if you can't do MSL first?

I'm certain that kind of conversation would come up. At the same
time, I would always remind everybody that unless you try, you're
just never going to know. That's the nature of this business. I
think it is where NASA really defines itself, and you need to try
these more difficult missions in order to find a way forward.

SPACE.com: Curiosity's power source could keep it roving
for many years. Are you prepared to be chief scientist for the
next decade, if it comes to that?

Grotzinger: That's a really good question
(laughs). Our prime mission is two years, and I think one has to
constantly keep in mind where the Mars
program is. For me personally, I'm thrilled to have the
opportunity to help lead the science team for the prime mission.
After that point, we'll see where we are.

If everything's going really well and we've made a lot of
discoveries and things are great, it may be appropriate for
somebody else to come in and steer the ship. And partly the
reason for that is, we may not have any other missions for people
to look forward to, and I think maybe it's time to evolve the
model by which we do these missions that go on for a decade in
order to create opportunities for other people to have some fun.

If, on the other hand, we're going along and it's been a tough
slog and yet there's real grounds for optimism but we haven't
really achieved the success that we were hoping for, I think I
feel the commitment to stick with it and follow through on the
strategic planning and the basis for the mission, and make sure
that we've really delivered what we think we can deliver.